2021 · Q1
The time elapsed between viewing a lightning flash and hearing the thunder of a cloud is 10 s. If the speeds of sound and light in air are 330 m/s and 3 x 10^8 m/s respectively, how far away is the storm?
general-sciencephysics-mechanics
- AAbout 1650 m
- BAbout 3300 m
- CAbout 990 m
- DAbout 1000 m
Explanation
Light from the flash reaches the observer almost instantaneously because its speed (3 x 10^8 m/s) is enormously greater than that of sound, so the 10-second delay is essentially the time sound takes to travel from the storm. Distance equals speed multiplied by time: 330 m/s x 10 s = 3300 m. Options A, C and D do not follow from this calculation. Hence the storm is about 3300 m away.